This invention relates to electrical machines employing liquid metal current collectors, and more particularly, to apparatus for maintaining electrical contact between the rotor collector ring and stator collector ring of a liquid metal current collector. A thin film of liquid metal is maintained at the innermost peripheral surface of a compliant brush which contains a continually-replenished supply of liquid metal.
In an acyclic machine using, instead of solid brushes, liquid metal current collectors in the shape of rings, the liquid metal forms a portion of the current-carrying loop. It is necessary for such current collectors to achieve adequate current collection at a current density in the liquid metal that is reasonable for that liquid metal material, so as to avoid excessive heating, and it is further desirable to minimize the area of liquid metal that contacts a relatively moving surface, so as to avoid excessive viscous drag, without requiring extremely tight tolerance in construction.
In B. D. Hatch application Ser. No. 838,714, filed Oct. 3, 1977 now U.S. Pat. No. 4,146,807, issued Mar. 27, 1979, and Ser. No. 23,809, filed Mar. 26, 1979 and both assigned to the instant assignee, liquid metal is contained within a raceway defined by a stator collector ring which includes a plurality of fins protruding radially-inward into a plurality of cage sectors, respectively, thereby essentially precluding expulsion of the liquid metal under the influence of Lorentz forces. In B. D. Hatch application Ser. No. 876,570, filed Feb. 10, 1978, now U.S. Pat. No. 4,168,446, issued Sept. 18, 1979, and assigned to the instant assignee, a narrow radial gap is maintained between each pair of rotor and stator collector rings, so that only a small quantity of liquid metal is required. Further, a compliant brush of electrically-conductive filaments is attached to the stator collector ring and extends to a position closely-adjacent the rotor collector ring, so that very little liquid metal will be expelled from the gap. The dimensional allowances for manufacturing and assembly tolerances, thermal expansion, etc., are compensated by the compliance of the brush, enabling the reduction in spacing between paired rotor and stator collector rings.
In my patent application Ser. No. 878,786, filed Feb. 17, 1978, now U.S. Pat. No. 4,186,321, issued Jan. 20, 1980, assigned to the instant assignee, and incorporated herein by reference, a collector is disclosed having a U-shaped brush of liquid metal-permeable conductive material attached to each stator collector ring and enclosing a volume of liquid metal between the stator and rotor collector rings. A thin film of liquid metal is maintained on the surface of the brush adjacent the tip of the rotor collector ring to complete contact between the rotor and stator.
The instant invention is a modification of my disclosed invention in the aforementioned U.S. Pat. No. 4,186,321. The instant invention describes brush structure to provide contact between the stator collector ring and rotor collector ring through the permeable braid or mesh, and a thin film of liquid metal maintained between the brush and the rotor contact surface. Therefore, contacts parallel or chamfered, or angled, relative to the centerline of the rotor shaft are maintained firmly in contact. My present invention will maintain the thin film gap of approximately 0.002 inch between the rotor collector and the brush throughout its length. The brush will remain substantially parallel to the rotor contact area throughout its circumference, so that no rounding of the braid at the edge of the rotor-stator contact area will occur, which could cause a larger than desired gap at the edges of the contact area. Thereby, the contact resistance is maintained low, and machine efficiency is maintained high.
Accordingly, one object of the instant invention is to provide a high efficiency, low loss current collector for a DC acyclic machine.
Another object is to provide a current collector which facilitates maintaining a constant gap between the rotor collector ring and the brush attached to the stator collector ring.